Method of saving string of tools installed in an oil well and a corresponding transmission assembly

ABSTRACT

In order to ensure that at least some of the tools ( 12 - 1 ) to  12 - 4 ) in a string of tools that is permanently installed in an oil well ( 10 ) are kept in operation even in the event of a localized fault, the link ( 18 ) interconnecting the tools and a surface installation ( 16 ) is subdivided into segments by switch members ( 20 ). More precisely, a switch member is associated with each tool. In addition, the link ( 18 ) forms a loop with both ends thereof being connected to the surface installation ( 16 ).

TECHNICAL FIELD

The invention relates to a method designed to enable at least a portionof a string of tools permanently installed in an oil well such as aproduction well to be saved in the event of a fault localized on one ofthe tools or on an electric cable connecting a surface installation toeach of the tools in series.

The invention also relates to a transmission assembly including anelectric cable connecting a surface installation in series to each ofthe tools of a string of tools installed permanently in an oil well, andorganized so as to enable such a method to be implemented.

STATE OF THE ART

In an oil well, a string of tools is generally installed permanently forthe purpose of measuring and controlling various characteristicmagnitudes of the well. Such a string of tools comprises a certainnumber of tools disposed in the well one above another at determineddepths. Each tool is independent of the others and is provided inparticular with means for measuring one or more magnitudes, or withmeans for controlling the flow of petroleum fluid along the well, orindeed with measurement means and with associated control means.

As a general rule, an electric cable connects a surface installation inseries to each of the tools in a string of tools constituted in thisway. The electric cable serves both to feed electricity to each of thetools and to transmit electrical signals from the surface installationto each of the tools, and vice versa.

In an existing arrangement, the link comprises two twisted conductorshoused in a stainless steel tube. In the surface installation, and alsoin each of the tools, signals are transmitted and received via atransformer. Electrical power is then supplied in common mode.

In that arrangement, which is characterized by a serial electrical linkbetween the surface installation and the various tools, an interruptionof an electrical conductor or the appearance of a short circuit willhave the consequence of making the entire string of tools inoperative.

U.S. Pat. No. 4,398,271 describes a system for transmitting data in aseismic streamer comprising a number of links, each of which includesswitch means. In use, the switch means are set to one of a number ofpossible positions to isolate discontinuities and form a continuous datapath.

SUMMARY OF THE INVENTION

A specific object of the invention is to provide a method enabling atleast a portion of a string of tools installed in an oil well to besaved in spite of a short circuit or an interruption occurring in thecable or in one of the tools.

According to the invention, this result is obtained by means of a methodof saving a string of tools installed in an oil well in the event of alocalized fault, a link connecting a surface installation in series witheach of the tools of said string, the method being characterized in thatit consists in subdividing the link into segments that are successivelyinterconnected by switch means, in locating a fault, if any, by closingeach of the switch means one after another starting from the surfaceinstallation until said fault appears, and in closing only those switchmeans that precede the last-closed switch means.

Because of the presence of switching means on the link, it becomespossible to save that portion of the string of tools which is situatedabove the location where the fault has occurred, by leaving open thelowest switching means connecting the surface installation to the faultytool or segment.

In a preferred implementation of the invention, a link is used thatforms a loop between the surface installation and the tools. Said faultis located by closing the switch means in both directions along saidloop from the surface installation, and in each direction only theswitch means preceding the last-closed switch means are closed.

Preferably, switch means are associated with each of the tools.

Advantageously, each tool is caused to communicate separately with eachof the two segments that are interconnected by the switch meansassociated with said tool.

By means of these characteristics in combination, it is possible eitherto keep all of the tools in operation when the fault has occurred on asegment interconnecting two tools, or else to put only one of the toolsout of circuit when the fault has occurred within said tool.

In a preferred implementation of the invention, the link comprises anelectric cable. In which case, advantageously, the tools are powered incommon mode while signals are simultaneously being interchanged betweenthe surface installation and each of the tools over a two-conductorcable.

The invention also provides a link connecting a surface installation inseries with each of the tools of a string of tools installed in an oilwell, which assembly is characterized in that the link is made up ofsuccessive segments that are interconnected by switch means suitable forbeing opened to isolate at least one faulty tool or cable segment.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described below by way ofnon-limiting example with reference to the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic vertical section view showing a transmissionassembly of the invention associated with a string of tools permanentlyinstalled in a borehole; and

FIG. 2 is a view comparable to FIG. 1, showing a variant implementationof the transmission assembly.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

In FIG. 1, reference 10 designates an oil well in production.

A string of tools is placed in the oil well 10 to perform measurementand control therein for well-operating purposes. In the embodiment shownby way of example, the string of tools comprises four tools numbered12-1 to 12-4 starting from the surface and installed in the well atdifferent depths, one above another.

As shown for the tool 12-3 only, in order to simplify FIG. 1, each ofthe tools 12-1 to 12-4 has an active portion 14. Depending on the natureof the tool in question, the active portion 14 may have one or moresensor(s), one or more actuator(s), or both sensors and actuators. Thetool also includes an electronics module serving to transmit signals inone direction or the other and also to transmit various commands.

The tools 12-1 to 12-4 are interconnected and are also connected to asurface installation 16 by means of an electric cable 18. In theembodiment shown, the electric cable 18 has two, preferablytwisted-together, electrical conductors 19 disposed inside a stainlesssteel tube (not shown) for protecting the electrical conductors 19.

More precisely, the link 18 connects the surface installation 16 inseries to each of the tools 12-1 to 12-4, and in this case does so inthe same order as the order in which the tools were installed inside thewell 10.

As shown solely for the tool 12-3, to simplify the figure, switch means20 are associated with each of the tools 12-1 to 12-4 so as to subdividethe link 18 into successive segments that are interconnected by theswitch means 20.

In the embodiment shown where the cable 18 has two electrical conductors19, each of the switch means 20 has two switches each located in arespective one of the electrical conductors.

At a first end of the cable 18, the two electrical conductors 19 areconnected to the secondary winding of a transformer 22 that forms partof the surface installation 16. The primary winding of the transformer.22 is connected to signal transmitter means 23 and receiver means 24.

The surface installation 16 also has a common mode electrical powersupply source 25 connected to the midpoint of the secondary winding ofthe transformer 22. Means for closing the electrical power supplycircuit are represented diagrammatically by a switch 26.

As shown solely for the tool 12-3, to simplify FIG. 1, each of the tools12-1 to 12-4 includes a transformer 28 whose primary winding iselectrically connected between the electrical conductors 19 of the cable18, upstream from the switch means 20 of the tool in question, i.e.vertically towards the top of the well relative to said switch means.The secondary winding of the transformer 28 fitted to each of the toolsis electrically connected to the active portion 14 associated with saidtool via transmitter means 30 and receiver means 29.

Each transformer 28, in association with the link 18, thus serves totransmit signals between the surface installation 16 and the tool inquestion. More precisely, each transformer 28 serves to transmit signalsfrom the surface installation 16 to the active portion 14 of thecorresponding tool. Conversely, each transformer 28 also serves totransmit signals from the corresponding tool 12-1 to 12-4 to the surfaceinstallation 16.

In addition, each of the tools 12-1 to 12-4 has an electrical powersupply circuit 32 connected to the midpoint of the primary winding ofthe transformer 28 associated with the tool. The assembly thus makes itpossible to power each of the tools 12-1 to 12-4 in common mode from anelectrical power supply source 25 located in the surface installation16.

The transmission assembly described above makes it possible, in theevent of a short circuit or of an interruption occurring in one of thetools or in one of the segments of the cable 18 between two tools, tosave all of the tools that are situated above the faulty element.

Thus, assuming that a short circuit or an interruption has occurred onthe segment of cable 18 that interconnects the tools 12-3 and 12-4, thenthe tools 12-1 to 12-3 can be kept in action by closing the switch meansassociated with the tools 12-1 and 12-2 and by opening the switch means20 associated with the tool 12-3. In which case only the tool 12-4 isinoperative.

Assuming that the interruption or short circuit has taken place insideone of the tools, such as the tool 12-3, then all of the tools situatedthereabove can continue to be used, by leaving the switch means 20associated with the tool 12-2 open and by closing the switch meansassociated with the tools situated thereabove, i.e. in this case thetools 12-1. On this assumption, all of the tools situated above thefaulty tool can continue to be used, while the faulty tool and the toolssituated beneath it are inoperative.

In the absence of a fault, all of the switch means 20 are normallyclosed, as is the switch 26. Under such circumstances, all of the tools12-1 to 12-4 are operative.

When a fault occurs, it is immediately detected by the signaltransmitter means 23 and receiver means 24 connected to the secondarywinding of the transformer 22. A command to open the switch 26 and allof the switch means 20 is then issued.

The fault is then located by closing the switch means 20 associated witheach of the tools 12-1 to 12-4 one after another until the faultreappears.

More precisely, signals are sent to the first tool 12-1 from the surfaceto find out whether it is operating properly. When the surfaceinstallation receives signals confirming such proper operation, theswitch means 20 associated with this first tool are closed.

If this closure causes the fault to reappear, then the fault is locatedeither in the segment of cable 18 interconnecting the tools 12-1 and12-2, or else in the tool 12-2. Under such circumstances, none of theswitch means 20 can be kept in the closed state, and only the tool 12-1remains usable.

Otherwise, i.e. if no fault occurs when the switch means 20 associatedwith the first tool 12-1 is closed, then the operations previouslyperformed on the tool 12-1 are repeated on the following tool 12-2. Whenthe tool 12-2 is found to be in working order, the corresponding switchmeans 20 are closed.

As before, this closure can either cause the fault to reappear, or cangive rise to no new fault.

These operations are repeated step by step until the fault is indeedlocated. After the previously closed switch 26 and switching means 20have been opened again, the switch 26 is reclosed as are all of theswitch means 20 preceding the previously last-closed switch means thatled to the fault being detected.

In FIG. 1, there is shown a preferred embodiment of the invention whichprovides considerably more effective tool saving. To this end, the link18 is not terminated at the deepest tool 12-4, but hereafter rises backup the well to the surface installation 16. In other words, the link 18forms a loop going from the surface installation 16 via each of thetools 12-1 to 12-4 in succession, and then returning to the surfaceinstallation 16.

In this case, and as shown diagrammatically in FIG. 1, the surfaceinstallation 16 is arranged so as to enable the tools 12-1 to 12-4 to bepowered and so as to enable signals to be transmitted via either of thetwo ends of the cable 18 that are connected to the installation 16. Tothis end, the surface installation 16 has a second transformer 22′ whosesecondary winding is connected to the second end of the cable 18 and isconnected across its two electrical conductors 19. The primary windingof the transformer 22′ is connected to signal transmitter means 23′ andreceiver means 24′.

To enable each of the tools 12-1 to 12-4 to be powered electrically fromthe second end of the cable 18, the midpoint of the secondary winding ofthe transformer 22′ is electrically connected to an electrical powersupply source 25′ via means for closing the power supply circuit andrepresented by a switch 26′.

It should be observed that in practice, the various elements of thesurface installation 16 connected to each of the ends of the electriccable 18 can have various portions in common, unlike the diagrammaticillustration of FIG. 1.

In this preferred embodiment of the invention, each of the tools 12-1 to12-4 also has means enabling electrical power to be delivered andelectrical signals to be transmitted downstream of the switch means 20fitted to the tool in question.

Thus, and as shown solely for the tool 12-3, in order to simplify thefigure, each of the tools then includes a second transformer 28′ whoseprimary winding is connected between the two electrical conductors ofthe cable 18 downstream from the switch means 20 of the tool inquestion, i.e. beneath the switch means. The secondary winding of eachof the transformers 28′ is then connected to the active portion 14 ofthe stage in question via transmitter means 30′ and receiver means 29′.This arrangement makes it possible to ensure that signals can betransmitted in either direction between the elements of the surfaceinstallation 16 connected to the second end of the cable 18 and the toolin question, even when the switch means 20 of the tool in question areopen.

In addition, the midpoint of the primary winding of the transformer 28′associated with each of the tools is connected to electrical powersupply means 32′ of the tool in question. This arrangement makes itpossible to power the tool electrically from the second end of the cable18 when the switch means 20 fitted to the tool are open.

In this preferred embodiment of the invention, all of the tools can bekept active in the event of a short circuit or an interruption occurringin any one of the segments of the cable 18 interconnecting any two tools12-1 to 12-4. The switch means 20 of two of the tools such as 12-2 and12-3 situated at opposite ends of the segment in question are then putinto the open state while all of the other switch means are closed.Under such conditions, the tools such as 12-1 and 12-2 situated abovethe faulty cable segment are powered and electrically connected to thesurface installation 16 via the portion of the cable 18 that is situatedabove the faulty segment. In addition, the tools such as 12-3 and 12-4that are situated beneath the faulty segment are electrically poweredand connected to the surface installation 16 via the other portion ofthe cable 18, connecting the bottom tool 12-4 to the surfaceinstallation.

If the fault lies within one of the tools, such as the tool 12-2, thenall of other tools, i.e. in this case the tools 12-1, 12-3, and 12-4,can be kept in working order.

To this end, the switch means 20 associated with the tools adjacent tothe faulty tool, such as 12-1 and 12-3 in this case, are kept open whilethe other switch means 20 are kept closed, e.g. the switch meansassociated with the tool 12-4, with this being done by acting on thecorresponding end of the cable.

The procedure is identical to that described above when the cable 18does not form a loop. The only exception is that it is effected in thiscase from each of the two ends of the able 18.

In the embodiment described with reference to FIG. 1, the tools 12-1 to12-4 of the string of tools installed in the well 10 are connected inseries in the same order as that with which they are to be found insidethe well. However, in a variant, as shown diagrammatically in FIG. 2,this method of connection is merely one particular non-limiting example.

Thus, in FIG. 2, the first end of the cable 18 from the surfaceinstallation 16 connects said assembly in series successively to the toptool 12-1, to the tool 12-3, then to the tool 12-4, prior to coming backup the well via the tool 12-2 and up to the surface installation 16.

Any other mode of serial connection involving all of the tools in thestring of tools, regardless of how many tools are involved, could beadopted without going beyond the ambit of the invention.

It should be observed that although it is preferred to power all of thetools in common mode as described above, it is also possible to powerthe tools separately from signal transmission by providing the cablewith a third electrical conductor. Under such circumstances, each switchmeans will also have a switch placed in said third conductor.

On the same lines, the technique used for transmitting signals betweenthe surface installation and each of the tools can also be replaced byany equivalent technique without going beyond the ambit of theinvention.

Finally, the invention is not limited to the case where the tools andthe surface installation are interconnected by an electric cable. On thecontrary, it applies to any type of link, for example a hydraulic link.

What is claimed is:
 1. A method of saving a string of tools installed inan oil well in the event of a localized fault, a link (18) being used toform a loop between a surface installation (16) and each of the tools(12-1 to 12-4) of said string, the method comprising the steps of:subdividing the link (18) into segments that are successivelyinterconnected by switch means (20), locating a fault, if any, byclosing each of the switch means (20) one after another in bothdirections along said loop starting from the surface installation (16)until said fault appears, opening said switch means (20) again, andre-closing in each direction only those switch means (20) that precedethe switch means last closed before the fault appeared.
 2. A methodaccording to claim 1, in which each tool (12-1 to 12-4) is caused tocommunicate separately with each of the two segments that areinterconnected by the switch means (20) associated with said tool.
 3. Amethod according to claim 1, in which said link comprises an electriccable (18).
 4. A method according to claim 3, in which tools are poweredin common mode while signals are simultaneously interchanged between thesurface installation (16) and each of the tools (12-1 to 12-4) over atwo-conductor cable (18).
 5. A transmission assembly, comprising: asurface installation (16), a series of tools (12-1 to 12-4) connected inseries to the surface installation (16) by means of a link (18) made upof a series of successive segments interconnected by switch means (20)capable of isolating a faulty segment; wherein the tools (12-1 to 12-4)are permanently installed in an oil well (10), and the link (18) forms aloop and provides both power and signals between the tools (12-1 to12-4) and the surface installation (18).
 6. An assembly according toclaim 5, wherein each tool (12-1 to 12-4) communicates separately witheach of two adjacent segments interconnected by the switch means (20)associated with said tool.
 7. An assembly according to claim 5, in whichsaid link comprises an electric cable (18).
 8. An assembly according toclaim 7, in which the cable (18) has two conductors and the surfaceinstallation (16) has a transformer (22, 22′) whose primary winding isconnected to signal transmitter and receiver means and whose secondarywinding is connected in series between the two conductors of the cable,the surface installation (16) also comprising an electricity source (25,25′) connected to the midpoint of the secondary winding.